In a medium bowl, beat mascarpone cheese and confectioners' sugar until smooth.

Place one cake layer upside down on a serving platter and prick top several times with a fork. Pour half of coffee mixture slowly over top, allowing it to absorb into cake. Spread cheese mixture evenly over layer, then place second cake layer right side up over cheese mixture. Prick top of second cake layer several times with a fork and pour remaining coffee mixture over top. Frost side and top of cake with whipped topping. Place split ladyfingers around side of cake, with flat sides pressing into frosting, then sprinkle top with cocoa.

Cover loosely and chill at least 4 hours before serving.

Notes: Mascarpone cheese is a soft, sweet Italian cheese, similar in consistency to soft cream cheese. Commonly used in dips and in sweet dishes like tiramisu, it's generally found in the cheese section of the supermarket.